Without the tables shared nor the error code it's hard to reproduce your example. But keep in mind that you need to perform this operation on geometries. You might try calling .geometry()
on your FeatureCollections.
A working example:
var geometry_a = ee.Geometry.Polygon([[1.597,43.897],
[0.0818,43.060],
[1.680,42.77],
[1.175,41.96],
[2.603,42.044],
[2.328,42.89],
[2.641,43.46],
[2.586,44.10],
[1.718,43.54],
[1.597,43.897]])
var geometry_b = ee.Geometry.Polygon([[-1.280,43.268],
[0.400,42.32],
[1.66,41.6],
[2.61,42.4],
[1.83,43.74],
[0.290,43.4],
[-1.28,43.26]])
var symetric_diff = geometry_b.symmetricDifference(geometry_a)
Map.addLayer(geometry_a, {color: 'red'}, 'geometry_a', true, 0.5)
Map.addLayer(geometry_b, {color: 'blue'}, 'geometry_b', true, 0.5)
Map.addLayer(symetric_diff, {color: 'green'}, 'symetric_diff', true, 1)
The two mockup geometries:

The symmetric difference:
